Practice question

In eukaryotes, precursor ribosomal RNA transcribed as forty-seven S transcript in nucleolus undergoes extensive covalent base modifications essential for ribosome assembly, stability, and decoding accuracy. Modifications include about one hundred 2'-O-methylations and one hundred pseudouridylations guided not by protein enzymes recognizing sequence alone but by small nucleolar RNAs snoRNAs providing sequence complementarity to target site and positioning catalytic proteins fibrillarin for methylation and dyskerin for pseudouridylation. SnoRNAs are intron-encoded, highly abundant within dense fibrillar component of nucleolus where rRNA transcription and early processing occur coordinated with assembly factors.